This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 52 964.3, filed on Oct. 26, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to a system for extinguishing a fire that has broken out in an enclosed space, such as the passenger cabin or a freight compartment in a passenger aircraft, and then achieving ongoing fire suppression.
A great variety of different systems using different extinguishing agents are known for fighting fires, i.e. extinguishing and/or suppressing fires, in different situations or applications. For example, at the present date, fires in aircraft are typically combated by a space flooding system using Halon 1301 as the extinguishing agent. In the field of fire protection in buildings and in marine applications, systems using water sprinklers or spray nozzles, or carbon dioxide (CO2) extinguishing systems are typically used. In various industrial applications, and especially in spaces containing sensitive electronics or other technical equipment, for example computer systems and installations, fire extinguishing is now typically carried out by means of carbon dioxide (CO2) since the use of Halon has been banned.
A method and system for suppressing or extinguishing a fire in an enclosed space is described in the German Patent Laying-Open Document DE 100 51 662 A1 (published May 8, 2002), and in the corresponding counterpart U.S. Published Application U.S. Ser. No. 2002/0070035 A1 (published Jun. 13, 2002), the entire disclosure of which is incorporated herein by reference. In the system and method according to that publication, nitrogen is introduced into the enclosed space in order to displace the oxygen required for sustaining the fire, whereby the fire is extinguished and/or suppressed. Particularly, the method and system according to the above publication aim to achieve a rapid extinguishing of the fire as well as an ongoing fire suppression in the enclosed space during a nearly unlimited time period after a fire has broken out. After detection of a fire in the enclosed space, the initial concentration of the nitrogen inert gas within the enclosed space is rapidly increased in a sudden shock-like manner, such that the oxygen content in the air within the enclosed space is rapidly reduced to a maximum oxygen concentration that is effective for extinguishing the fire. Preferably, the oxygen content within the enclosed space is reduced to and maintained at approximately 12 vol. %. Then, for maintaining this maximum oxygen concentration effective for fire extinguishing or suppression, nitrogen is continuously supplied in a prescribed quantity or prescribed rate into the enclosed space. To provide these two different phases or rates of supplying nitrogen, the system preferably includes nitrogen tanks or nitrogen generators to rapidly supply a limited quantity of nitrogen with a high flow rate, as well as a membrane system to supply an essentially unlimited quantity of nitrogen for a long duration at a lower supply rate.
Published European Patent Application EP 0,234,056 A1 discloses an extinguishing system for extinguishing a fire that has broken out in a passenger cabin or a cargo space of a passenger aircraft. The disclosed fire extinguishing system includes a supply container for storing and supplying pressure-liquified Halon, which may be supplied from the container through a duct system to extinguishing nozzles arranged in the passenger cabin or the cargo space. Thus, the Halon is supplied through the extinguishing nozzles into the cabin or the cargo space in order to establish an effective concentration thereof for extinguishing the fire in a relatively short time.
German Patent DE 41 22 446 C2 discloses a system for fire and explosion prevention, as well as breathing air supply for personnel, in armored vehicles such as military tanks. This system includes an air separating device that separates an airflow of the ambient air into a first oxygen enriched airflow that is provided to air breathing masks for the armored vehicle personnel, and a second nitrogen enriched airflow that is delivered into the interior space of the vehicle as well as interior spaces of containers therein, for fire and explosion prevention, whereby air inlets are connected to the respective spaces.
German Patent DE 198 24 300 C1 discloses a fire suppression system for rapidly evolving and progressing fires in a volume space that is to be monitored, which comprises one or more extinguishing agent containers, which contain a gaseous halogenated hydrocarbon as the extinguishing agent. The system further includes a monitoring and control arrangement that monitors the volume space and accordingly controls the fire suppression system, e.g. to actuate the system so as to distribute the extinguishing agent into the volume space through respective extinguishing agent distributor nozzle arrangements connected to the extinguishing agent storage containers.
U.S. Pat. No. 4,643,260 (Miller) discloses a fire suppression system including two Halon storage bottles, wherein the first bottle relatively rapidly discharges Halon and the second bottle relatively slowly discharges Halon, in order to rapidly achieve an initial higher Halon concentration and to thereafter maintain a somewhat lower Halon concentration in the enclosed space in which a fire is to be suppressed. The disclosed system also includes a molecular sieve as a filter and dryer in the duct between the second bottle and a flow regulator, to trap particles and to adsorb water from the extinguishant.
While the above described systems have all been found to be effective at extinguishing or suppressing fires in enclosed spaces, it has been found that improvements are still possible, particularly in view of the special considerations that apply for fire suppression and extinguishing in an aircraft. For example, Halon systems necessarily have a limited supply of the Halon extinguishing agent, so they are able to provide fire suppression for only a limited duration. Also, carrying along the stored Halon supply is a constant weight penalty, which is a critical consideration in the operation of a commercial aircraft. The Halon agent is also relatively expensive, and presents health risks at high concentrations. On the other hand, the Halon agent has been found to be fast-acting and highly effective at extinguishing and suppressing fires in enclosed spaces. In comparison, a fire suppression system using only nitrogen as the extinguishing agent is generally not as rapidly acting, and the nitrogen must be provided in a higher concentration (in comparison to Halon) in the enclosed space in order to be effective. Advantageously, however, the nitrogen gas as an extinguishing agent can be continuously provided in an essentially unlimited quantity, and does not need to be stored and carried constantly in the aircraft. There is no known fire combating system that avoids the various disadvantages, yet achieves the various advantages of the different known fire suppression and extinguishing agents.
In view of the above, it is an object of the invention to provide a system and method for extinguishing and suppressing fires in an enclosed space, which uses different extinguishing agents in combination or in succession. It is a further object of the invention to provide a fire extinguishing and suppression system and method that achieve a rapid fire extinguishing or flame knockdown, together with a long-term continuous fire suppression thereafter. The invention further aims to avoid or overcome the disadvantages of the prior art, achieve the advantages of the prior art, and achieve additional advantages, as apparent from the present specification. The attainment of these objects is, however, not a required limitation of the claimed invention.
The above objects have been achieved according to the invention in a system and method for extinguishing and suppressing a fire in an enclosed space, such as a passenger cabin or a freight or cargo hold in an aircraft. Throughout this specification, the terms xe2x80x9cfire extinguishingxe2x80x9d and xe2x80x9cfire suppressionxe2x80x9d both refer to the acts of reducing or entirely putting-out a fire, and do not absolutely require entirely putting-out a fire. Generally, the term xe2x80x9cfire extinguishingxe2x80x9d refers to the initial flame knockdown and reducing the intensity of an existing fire, and the term xe2x80x9cfire suppressionxe2x80x9d refers to the further reduction, the prevention of renewed flare-ups, and the prevention of further spreading of a fire, after the initial flame knockdown and fire extinguishing. The term xe2x80x9cenclosed spacexe2x80x9d does not require absolute complete enclosure or hermetic sealing of the space, but rather refers to any space that is sufficiently enclosed to be able to establish and maintain a specified gas atmosphere therein. The term xe2x80x9cductxe2x80x9d refers to any duct, pipe, hose, channel, conduit, tube, or the like that is suitable for conveying a gas therethrough.
According to the invention, the fire extinguishing and suppression system includes extinguishing nozzles arranged in the enclosed space, a Halon storage container that contains a Halon or a Halon substitute as a first extinguishing agent, a nitrogen generator that provides nitrogen or a nitrogen-containing gas as a second extinguishing agent, and a duct system that connects the Halon storage container and the nitrogen generator to the extinguishing nozzles. With this system, the first extinguishing agent (e.g. Halon), and the second extinguishing agent (e.g. nitrogen-containing gas) can be supplied together, in succession, or in alternation through the extinguishing nozzles into the enclosed space, in order to extinguish and then suppress a fire detected in the enclosed space. Particularly, the Halon is delivered first to rapidly extinguish the fire in the enclosed space, and the nitrogen-containing gas, and especially nitrogen enriched air, is delivered for a long time following the detection of a fire in order to displace the oxygen required for maintenance of the fire, so as to achieve a long-term fire suppression in the enclosed space.
According to preferred detailed embodiment features of the invention, the nitrogen generator can be embodied as an air separation module, especially comprising a molecular sieve, that separates an inlet flow of air into a nitrogen enriched airflow as the second extinguishing agent, and an oxygen enriched airflow that can be exhausted or delivered to breathing gas masks. The inlet airflow of the air separation module can be provided by bleed air from an aircraft engine, or from a blower of an aircraft air conditioning system.
The first extinguishing agent comprises a Halon (such as Halon 1301(TM)xe2x80x94trifluorobromomethane, bromotrifluoromethane; or Halon 1211(TM)xe2x80x94bromochlorodifluoromethane) or an adequate, tested, and accepted Halon substitute (for example FM200/FE36). Advantageously according to the invention, the concentration of the first extinguishing agent effective for fire extinguishing or suppression can be established within a relatively short time in the enclosed space. This effective fire extinguishing concentration of Halon or a Halon substitute is very small relative to the effective fire extinguishing concentration of other extinguishing agents such as carbon dioxide, argon, or nitrogen. Thus, the initial introduction of the first extinguishing agent (e.g. Halon) achieves the initial flame knockdown or extinguishing of the fire rather quickly, i.e. once the first extinguishing agent has become distributed uniformly throughout the enclosed space to achieve the required effective fire extinguishing concentration thereof.
During the introduction of the first extinguishing agent, or following the uniform disbursement thereof in the enclosed space, the second extinguishing agent comprising a nitrogen-containing gas or nitrogen enriched air is introduced into the enclosed space to establish an effective fire extinguishing or suppressing concentration of nitrogen and a corresponding effective low concentration of oxygen in the enclosed space. This advantageously provides a continuous long-term fire suppression.
The result is a mixture of gas in the enclosed space, comprising the Halon or Halon substitute gas and nitrogen enriched air. At every point in time during the fire suppression phase, the concentration of this gas mixture must be maintained above a certain minimum concentration, and correspondingly the concentration of oxygen in the enclosed space must be maintained below a certain maximum oxygen concentration, so as to achieve the desired fire suppression. The extinguishing system must thus be dimensioned, configured and designed to initially establish and essentially continuously maintain the required mixed gas concentration in the enclosed space, in consideration of the given volume of the enclosed space.
As an example application of the inventive fire extinguishing and suppressing system to combat a fire in a freight or cargo compartment of an aircraft, a fire combating process can be carried out, for example, as follows. Any conventional fire detection system initially detects the existence of a fire, and initiates a corresponding fire alarm signal to alert the cockpit crew. In response thereto, the cockpit crew activates the fire extinguishing and suppressing system. Under certain extreme conditions, the fire extinguishing and suppressing system could be activated automatically by the fire detection system, without intervention or action by the cockpit crew. Upon activation, the fire extinguishing and suppressing system introduces Halon 1301 or a Halon substitute gas into the cargo compartment to establish the prescribed effective design concentration of Halon therein. Simultaneously, or at a time delay after the introduction of the first extinguishing agent (Halon), or after a sensor senses that the required concentration of Halon has been established or that the concentration of Halon is diminishing, the nitrogen generator is activated so that the air separation module supplies nitrogen enriched air into the cargo compartment so as to make the environment therein inert. Nitrogen enriched air is continuously supplied from the nitrogen generator into the cargo compartment to achieve ongoing extinguishing and/or suppression of the fire until the aircraft lands and ground-based fire fighting equipment and crews take over the further fire fighting efforts.
With the above features, the invention achieves a combination of many of the advantages of various prior art fire extinguishing systems, while avoiding most of the disadvantages thereof. For example, the invention uses only gaseous extinguishing agents, which ensures a good distribution of the extinguishing agent throughout the enclosed space, without leaving behind any residues, moisture or other contamination in the enclosed space. This avoids the need of complex, time consuming and costly cleaning efforts in the event of an inadvertent unnecessary triggering of the fire extinguishing system. Another advantage is the on-board generation of the second extinguishing agent during the operation of the system, so that it is unnecessary to store a large amount of the extinguishing agents, while still achieving very long (essentially indefinite) fire suppression durations with a comparatively small overall system mass. On the other hand, the limited quantity of the first extinguishing agent is rapidly available to rapidly initiate the fire extinguishing process, in combination with the long-term availability of the second extinguishing agent which is continuously generated and supplied during the process. The use of environmentally friendly extinguishing agents is also advantageous.